When constructing oil or water conduits, drainage courses, communications and/or electrical transmission and distribution lines, it is often necessary to bore or drill holes in rock disposed under roadways and/or building foundations, without disturbing the structural integrity of such foundations.
To drill such holes, it is common to dig a shaft on either side of the foundation or structure, and by means of an auger in soft ground or a rock drill in harder ground, drive the auger or drill from shaft to shaft. This is typically accomplished via conventional drilling techniques that push the auger or rock drill, most often by utilizing a rotary drill string. The auger or drill, and the trailing drill string, are inserted in sections and driven from one of the shafts to the other.
Typically, such boring or drilling is carried out by a drill head having one or more drill bits, or bit segments, with a means for driving the bits/segments, wherein the driving mechanism typically utilizes fluid power or, alternately, is mechanically driven.
The driven drill head is often a rotary bit having cutting surfaces thereon, wherein the cutting surfaces ‘grind away’ at a selected rock face. In addition to rotary drills, percussive bits are often selected for performing the cutting operation. Such percussive bits operate by impact, and are typically driven by either mechanical force or by the force of pressurized air. Still other bits incorporate combined rotation and percussion in operation thereof.
It is often necessary to enlarge a hole once drilled, or to bore a large hole by successive passes with a reamer after first drilling a pilot hole. For drilling narrow diameter holes, a simple, single drill will often suffice. However, for larger diameter holes it is often necessary to begin by drilling a smaller pilot bore and then increasing the diameter of the bore by successively pulling reamers of increasing diameter through the bore.
Additionally, while drilling, material removed from a rock face must somehow be removed. Unfortunately, a single rotational or percussive drill bit fills the full diameter of the hole drilled and, thus, leaves little room for clearance of material from the dirt or rock face that the drill bit is cutting. Failure to clear the debris from the hole results in packing of the debris, and, thus, leads to clogging and binding of the drill bit. Accordingly, drill bits, or bit segments, are often grouped together to form a cutting surface with space available for removal of the debris that accumulates from the cutting operation. Such a device utilizing a cluster of circular rotational and percussive drill bits is described in the U.S. Pat. No. 4,878,547 to Lennon. Unfortunately, however, the device of Lennon '547 lacks airflow suitable to remove debris from the rock face being cut.
A cluster of air-driven percussive drill bit segments is disclosed in the U.S. Pat. No. 6,467,558 to Miyamoto et al. Since it is still necessary to clear debris from the rock face and prevent accumulation of debris, air is often utilized where the percussive bit is mechanically driven. Miyamoto et al. '558, discloses air transmission tubes formed around the central shaft of the drill bit in order to bring air to the rock face. While the device of Miyamoto et al. '558 utilizes air flow, the air flows out of the tubes surrounding the bit segments, not out of the sides of the bit segments themselves, and thus, does not facilitate clearing of debris from the gaps between the bit segments. Accordingly, Miyamoto et al '558 utilizes scalloped areas to permit debris removal and prevent clogging of the bit segments.
Moreover, due to the space between the bit segments of the Miyamoto et al. '558 device, and the scalloped areas of same, there is a reduced area available for active cutting surface, and as such, a reduction in operational efficiency.
If the gaps between bit segments can be closed together, larger surface area drill bit segments could be utilized, thereby increasing the cutting efficiency of the drill/reamer. However, as such gaps are closed to gain increased cutting surface area and its resultant more efficient spacing, there is a greater likelihood of binding and clogging of the bit segments due to debris finding its way in between the bit segments. Accordingly, some means must be utilized to remove debris from gaps between close-fitting segments.
Therefore, it is readily apparent that there is a need for a percussive reamer/drill bit and method of use thereof for facilitating the removal of debris from the gaps between the sides of bit segments, thereby permitting the bit segments to be placed closely adjacent one another, and thus increasing available cutting surface area and improving overall efficiency.